Sulfur scavenging materials

ABSTRACT

Materials which react with (“scavenge”) sulfur compounds, such as hydrogen sulfide and mercaptans, are useful for limiting sulfur-induced corrosion. Surface-modified particles incorporating a hexahydrotriazine moiety are disclosed and used as sulfur scavengers. These surface-modified particles are used a filter media in fixed filter systems and as additives to fluids including sulfur compounds. The hexahydrotriazine moiety can react with sulfur compounds in such a manner as to bind sulfur atoms to the surface-modified particles, thus allowing removal of the sulfur atoms from fluids such as crude oil, natural gas, hydrocarbon combustion exhaust gases, sulfur polluted air and water. The surface-modified particles may, in general, be sized to allow separation of the particles from the process fluid by sedimentation, size-exclusion filtration or the like.

This application is a divisional of co-pending U.S. patent applicationSer. No. 15/158,356, filed May 18, 2016, which is a divisional ofco-pending U.S. patent application Ser. No. 14/294,220, filed Jun. 3,2014, now U.S. Pat. No. 9,469,660. The aforementioned related patentapplications are herein incorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to materials that react with sulfur andsulfur-containing compounds, and more specifically to filtration andremoval of sulfur and sulfur-containing compounds from fluids.

Sulfur and sulfur-containing compounds are often unwanted impurities ina variety of contexts. For example, sulfur is typically the mostabundant element after carbon and hydrogen in crude oil. Sulfur in crudeoil may be in the form of hydrogen sulfide (H₂S) and/or thiols (alsoreferred to as mercaptans). These sulfur compounds, particularly H₂S,may cause corrosion of metal pipeline components, storage tanks, andprocessing equipment. Additionally, any sulfur that remains in end-usefuels and lubricants may cause corrosion of, or other damage to,end-user equipment (e.g., engines, boilers, bearings, etc.). Combustedfuels or materials that include sulfur ultimately contribute topollution as sulfur oxides (SO_(x)). Sulfur oxides cause harmfulenvironmental effects and are particularly significant as contributorsto air pollution. The various sulfur compounds emitted into theenvironment may corrode unprotected materials and be harmful to humanhealth.

A need exists for materials and methods for removing sulfur andsulfur-containing compounds from a fluid or otherwise protectingmaterials against corrosion caused by sulfur and sulfur-containingcompounds.

SUMMARY

In an embodiment of the disclosure, a surface-modified particleincluding a hexahydrotriazine moiety linked via covalent bonds to theparticle is described. The surface modified-particle may, in someembodiments, be used in processes and apparatuses for removal of sulfurcompounds from fluids.

In another embodiment of the disclosure, a method of making asurface-modified particle is described. The method includes exposing aninorganic particle having a hydroxyl reaction site thereon to a silaneincluding a primary amine group and exposing the inorganic particle toan aniline compound. In an exemplary embodiment, the method produces asurface-modified particle including a hexahydrotriazine moiety linkedvia covalent bonds to the particle.

In yet another embodiment of the disclosure, a method of removing asulfur compound from a fluid is disclosed. The method includes placing afluid including a sulfur compound in contact with a particle having ahexahydrotriazine moiety linked via covalent bonds thereto.

Fluids in this context may include, without limitation, liquids, gases,and mixed-phase flows, streams, solutions, mixtures, and suspensions.Sulfur compounds in this context includes, without limitation, hydrogensulfide (H₂S), thiols (R—SH, where R includes at least one carbon), andsulfur allotropes (e.g., “octosulfur” (S₈)). Aniline compounds in thiscontext includes, without limitation, amino-aromatic compounds.Amino-aromatic compounds in this context includes, without limitation,such molecules as aniline (C₆H₅NH₃) and N,N-dimethyl-p-phenylenediamine.

The above-described embodiments and other features and advantages of thepresent disclosure will be appreciated and understood by those skilledin the art from the following detailed description, drawings, andappended claims

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a surface-modified particle having a moiety that reactswith sulfur compounds.

FIG. 2 depicts an exemplary reaction scheme for producing asurface-modified particle having a moiety that reacts with sulfurcompounds.

FIG. 3 depicts ¹³C-NMR spectra reflecting formation of asurface-modified particle having a moiety that reacts with sulfurcompounds produced according to an exemplary reaction scheme.

FIG. 4 depicts a reaction between a hexahydrotriazine moiety and asulfur compound.

FIG. 5 depicts a) ¹H-NMR spectra of a reaction of a small molecule modelcompound having a hexahydrotriazine moiety and a sulfur compound, and b)a kinetic profile of the reaction the small molecule model compound andthe sulfur compound.

FIG. 6 depicts a filter including a surface-modified particle forremoving sulfur compounds from a fluid.

FIG. 7 is a flowchart depicting a first method for removing sulfurcompounds from a fluid.

FIG. 8 is a flowchart depicting a second method for removing sulfurcompounds from a fluid.

DETAILED DESCRIPTION

Small molecule compounds including, for example, triazine groups havebeen used as sulfur scavengers in crude oil production and refiningapplications. In general, while these small molecule compounds may reactwith sulfur compounds, such as H₂S, in the process fluid (e.g., crudeoil), additional process steps are often required to remove thesulfur-reacted small molecule compounds (and also possibly anyremaining, un-reacted small molecule compound) from the process fluid.Typically, these additional processing steps are energy intensive,complex, and/or costly. For example, distillation or solvent extractionmethods may be used to separate the spent scavenger molecules from theprocess fluid. It would be desirable to provide materials and methodsfor removing sulfur compounds which would not require distillation orsolvent extraction processes to separate spent and un-reacted sulfurscavenger molecules from the process fluid.

FIG. 1 depicts a surface-modified particle having a moiety that reactswith sulfur compounds according to an embodiment of the presentdisclosure. In FIG. 1, particle 100 has a sulfur-reactive moiety 120attached to a surface 101 thereof via a linkage 110.

In an embodiment, particle 100 is a silica (SiO₂) particle, but in otherembodiments particle 100 may comprised of other inorganic materials,including without limitation, glasses, ceramics, metal oxides, and thelike. Particle 100 may specifically comprise alumina (Al₂O₃) in someembodiments, for example. Particle 100 may comprise cellulose orcellulosic material in some embodiments. Particle 100 may be comprisedof a coated core or an interior of a first material and a surfacecoating comprising a second material or a surface treated to providereactive sites for linkage of the sulfur-reactive moiety 120 to thefirst material.

Particle 100 is depicted as having a spherical shape, but in general anyshape may be adopted. For example, particle 100 may be spherical,rod-like, disk-shaped, plate-shaped, ring-shaped, pipe-shaped, orirregular-shaped, without limitation. Particle 100 may also have variouspores, pits, or channels in its outer surface 101. Such pores, pits, orchannels may be regularly arrayed on outer surface 101 in specificpatterns or may be randomly disposed.

Particle 100 may be a portion of a coating or incorporated into acoating of a surface or a substrate. In some embodiments, particle 100may be a substrate having, or being treated to have, reactive sites(i.e., reactive with respect to a silane including a primary aminegroup). A substrate in this context may be, for example, an interiorsurface of a pipe, an exterior surface of a pipe, a countertop, asurface of a storage tank, a microelectronic component, a silicon wafer,a printed circuit board, or portions of the foregoing.

In an embodiment, particle 100 may be a nano-scale particle (1 nm-1000nm), however, in general, the particle 100 may be any of dimension(e.g., 1 nanometer (nm)-1000 millimeter (mm)) including macroscopicdimensions.

Linkage 110 connects sulfur-reactive moiety 120 to surface 101 ofparticle 100. In an embodiment, linkage 110 is formed using anaminosilane compound. Linkage 110 may, for example, include an alkylchain having 2 to 12 carbons or an aromatic linker. The alkyl chain mayhave one or more substituents attached thereto in addition tosulfur-reactive moiety 120. Linkage 110 could include a siloxane, anether, a sulfone, an ester, a carbonate, and/or an amide group inpolymeric, oligomeric, or otherwise, form. In some embodiment, linkage110 may comprise a siloxane chain or a poly(ethylene glycol) ether-type(PEG-ether) chain.

In an example embodiment, linkage 110 may be formed using(3-aminopropyl)triethoxysilane (APTES). In general, when particle 100 issilica the surface 101 will include silanol (—Si—OH) groups generated byreaction of atmospheric moisture with exposed silicon atoms. A reactionbetween a silane group and a surface 101 silanol group can be used tocovalently bond the silicon atom of the aminosilane compound to particle100. The amino group of the aminosilane compound can be used to providethe sulfur-reactive moiety 120.

Sulfur-reactive moiety 120 includes a trivalent hexahydrotriazine groupcorresponding to formula (1):

The substituents labeled “Ar” in FIG. 1 are aryl groups, for example.Without limitation, the “Ar” groups may correspond to a phenyl group ora N,N-dimethylamino-p-phenyl group. In general “Ar,” may correspond toany electron-donating group, such as without limitation, methyl ether(OMe), pyrene, aromatics, —OH (hydroxyl), —SH (sulfhydryl), —S—R(alkylthio, wherein R includes an alkyl group).

FIG. 2 depicts an exemplary reaction scheme for producing asurface-modified particle having a moiety that reacts with sulfurcompounds. A particle 100 has various —OH reaction sites on surface 101.When particle 100 is silica, particle 100 may be purposively exposed towater to promote the formation of the —OH reaction sites, thoughtypically mere exposure to normal atmospheric humidity will generatepotential —OH reaction sites on silica surfaces. When the particle 100is exposed to an aminosilane compound (e.g., APTES), the aminosilanecompound reacts with the —OH reaction site resulting in a covalentbonding of the silicon atom in the aminosilane compound and the oxygenatom of the —OH reaction site. Without being limited to any particularreaction mechanism, FIG. 2 depicts the reaction between APTES and the—OH reaction site as going through a silanol intermediary. Suchintermediary maybe be formed as distinct species or may be transitory.The intermediary may be formed in solution phase or at the surface ofparticle 100. After reaction with the aminosilane, particle 100 has anamino-functionalized compound attached to surface 101.

While a single —OH reaction on particle 100 is depicted as reacted inFIG. 2, many —OH reaction sites on particle 100 may ultimately reactwith available aminosilane compounds such that substantial portion ofsurface 101 may be covered with covalently bonded amino groups.

In an example embodiment, sulfur-reactive moiety 120 may be formed in areaction between amino-functionalized particle 100 and aniline(C₆H₅NH₂). The reaction between aniline and the primary amine groupattached to particle 100 produces a hexahydrotriazine group attached toparticle 100. Sulfur-reactive moiety 120 may also be formed in areaction between the amino-functionalized particle andN,N-dimethyl-p-phenylenediamine (DPD) corresponding to formula (2):

Other examples of an aniline compound which may be used to formsulfur-reactive moiety 120 include: p-methoxyaniline (MOA),N,N-dimethyl-1,5-diaminonaphthalene (15DMN),N,N-dimethyl-1,4-diaminonaphthalene (14DMN), and N,N-dimethylbenzidene(DMB), which have the following structures:

Reaction conditions for the formation of sulfur-reactive moiety 120 arein general between 22° C. and 200° C. in dimethyl sulfoxide (DMSO)((CH₃)₂SO) solvent. The solvent used in the formation reaction of thesulfur-reactive moiety 120 may be a polar aprotic solvent. Otherpotential solvents include, without limitation, acetonitrile,tetrahydrofuran (THF), N,N-Dimethylformamide (DMF), toluene, diethylether, propylene carbonate, chloroform,1,3-Dimethyltetrahydropyrimidin-2(1H)-one (DMPU), 1-Methyl-2-pyrrolidone(NMP), and N,N-Dimethylacetamide (DMAc).

FIG. 3 depicts ¹³C-NMR spectra reflecting formation of asurface-modified particle having a moiety that reacts with sulfurcompounds produced according to an exemplary reaction scheme. Theparticle in this example was silica. The linkage 110 was formed usingAPTES. Two different particle types were synthesized and evaluated. Afirst particle type includes a sulfur-reactive moiety 120 wherein “Ar”is a phenyl group and a second particle type includes a sulfur-reactivemoiety 120 wherein “Ar” is a N,N-dimethylamino-p-phenyl group. Formationof the hexahydrotriazine moiety in each case was performed in DMSO at50° C. The NMR spectra establish the formation of hexahydrotriazinesurface-functionalized silica particles.

Filtration of Sulfur Compounds

With reference now to FIG. 4, a compound including a hexahydrotriazine(HT) moiety may react with a sulfur compound as depicted. In thisinstance, the sulfur compound is H₂S, but thiol compounds will alsoreact with a hexahydrotriazine group. Under some reaction conditionsvarious sulfur allotropes, such as octosulfur (S₈, also referred to ascyclo-sulfur), may also react with HT materials.

In the reaction depicted in FIG. 4, the sulfur atoms replace two ofthree nitrogen atoms in the HT moiety, which results in the substituentattached to the two replaced nitrogen atoms (e.g., phenyl group,N,N-dimethylamino-p-phenyl group, etc.) being separated from (that is,no longer covalently bonded to) the hexahydrotriazine (HT) moiety. Ingeneral, reaction of the HT material with a sulfur compound thus resultsin attachment of sulfur atoms to the surface-modified particle 100. Assuch, particles 100 can be used as a reactive filtration media to removesulfur compounds from various fluids.

As a means to understand the reaction between HT functionalizedparticles and sulfur compounds, studies on small molecule modelcompounds have been performed. In general, the small molecule modelcompounds incorporate a hexahydrotriazine group but are not attached tothe surface of a particle. Reactions of the small molecule modelcompounds are typically easier to monitor and detect under controlledconditions than reactions involving surface-modified particles.

FIG. 5 depicts ¹H-NMR spectra of a reaction between a sulfur compound(H₂S) and small molecule model compound including a hexahydrotriazinemoiety (4,4′,4″-(1,3,5-triazinane-1,3,5-triyl)tris(N,N-dimethylaniline))(also referred to as SMC-HT). FIG. 5 shows several NMR spectra obtainedover time (with a 3.7 minute spacing).

In FIG. 5, the diagnostic singlet (a) corresponding to a hydrogen on thenitrogen-rich HT core is observed to decrease in intensity during thecourse of the reaction, while two new peaks (a′) and (a″) increase inintensity. The peaks (a′) and (a″) are considered to correspond to thehydrogen atoms on the diothiazine reaction product.

FIG. 5 also depicts the kinetic profile of the reaction between thesmall molecule compound (SMC-HT) and H₂S. The data in the kineticprofile is based on the ¹H-NMR measurements. After a period ofapproximately 37 minutes, the peak (a) is no longer observed in thespectrum, indicating substantially complete conversion of SMC-HT into adifferent compound, specifically a diothiazine compound in which twosulfur atoms have been incorporated in place of two ring nitrogens ofthe original SMC-HT. The triathiane product (corresponding to a reactionproduct in which all ring nitrogens in the SMC-HT are replaced withsulfur atoms) has not been observed experimentally under the studiedreaction conditions; however, preliminary density functional theorycalculations suggest the formation of triathiane is thermodynamicallyfavorable. Based on these preliminary results it is possible theformation of the triathiane product is kinetically disfavored over thetwo-sulfur (diothiazine) reaction product. In general, it is expectedthat the sulfur atoms will substitute with the aromatic amines ratherthan the nitrogen most directly linked to the particle because theelectronics of the aryl ring makes the aromatic amine(s) a betterleaving group and better able to stabilize the build-up of positivecharge on the adjacent carbon atom thought necessary for the sulfurexchanging reaction.

While a reaction between SMC-HT and hydrogen sulfide (H₂S) has beenevaluated, it is expected that other sulfur compounds would similarlyreact with a HT moiety.

Removal of Sulfur Compounds from Fluids

As described, HT moieties react with sulfur compounds in such a way thatsulfur becomes linked to the surface-modified particles incorporatingthe HT moiety. Upon reaction with HT moiety, the sulfur becomes attachedto the particle via covalent linkages. As such, surface-modifiedparticles incorporating HT moieties can be used as reactive filter mediafor removal of sulfur compounds from fluids. In various embodiments,such filtration media can be incorporated in a fixed-media filter devicesuch as an air intake filter for microelectronic fabrication facility orother pollution sensitive environment, an automotive fuel filter, anautomotive oil filter, a water treatment filter, a combustion exhaustfilter, or the like. In this context, a fixed-media filter device couldincorporate surface-modified particles incorporating a HT moiety by, forexample, filling a cavity with particles, embedding the particles in abinder resin or gel, incorporating the particles in a porous medium, andallowing or causing the particles to gelate or otherwise agglomerateinto a mass.

Alternatively, surface-modified particles may be added directly to thefluid from which sulfur compounds are to be removed. The added particlesand the fluid may later be separated by various methods, such as, forexample, fixed-filter filtration, settling, sedimentation, centrifuge,solvent partitioning, evaporative methods, distillation, or the like.The surface-modified particles may in some embodiments be included in afluidized bed apparatus—that is, the fluid to be filtered and thesurface-modified particles may be contacted with each other under flowand pressure conditions which cause the fluid-particulate mixture tobehave similarly to a fluid (fluidize).

FIG. 6 depicts a filter 600 including filter media 610. Filter media 610may be comprised of surface-modified particles 100 incorporating a HTmoiety. Filter media 610 is disposed in a filter body 620. It should benoted that FIG. 6 is a schematic depiction that is not necessarily toscale and, as such, filter media 610 may be any size relative to filterbody 620. Indeed, in various embodiments, filter media 610 may includeparticles having nano-scale dimensions. Filter body 620 may be packedwith filter media 610 or filter media 610 may comprise loose particleswhich move within filter body 620. Alternatively, a portion of filterbody 620 may be packed and a different portion may include looseparticles. A filter body 620 packed or filled with particles may providea filter media 610 having tortuous fluid pathways to promote contactbetween the fluid and filter media 610.

As depicted, filter 600 receives a fluid from source 650 through processfluid inlet 630. The process fluid includes sulfur compounds and isfiltered by contact with filter media 610 within filter body 620. Afterpassing through filter body 620, the fluid is output from process fluidoutlet 640 to environment 660.

As noted, filter media 610 may include a surface-modified particle 100incorporating a HT moiety. Filter media 610 may comprise monodispersesurface-modified particles 100 (particles with approximately the samedimensions or a narrow distribution of sizes). Filter media 610 mayalternatively comprise surface modified particles 100 having manydifferent nominal sizes or any statistical distribution of particlesizes. The surface-modified particles 100 may each have the same type ofsurface functionalization or there may be different types of surfacefunctionalized particles 100. That is, for example, some particles 100may incorporate phenyl groups and other particles 100 may incorporateN,N-dimethylamino-p-phenyl groups.

Filter media 610 may in some embodiments include particles or materialintended to filter fluid components other than sulfur compounds. Forexample, filter media 610 may incorporate a mesh or fabric to filtermacroscopic particles, grit, and dust. Filter media 610 may alsoincorporate materials which react with or otherwise sequester variousdissolved metal components in the process fluid.

Source 650 may be anything that supplies, outputs, generates, orcontains a fluid including sulfur compounds. For example, source 650 maybe a crude oil reservoir, a natural gas storage basin, a liquefiednatural gas (LNG) production facility, a petroleum refinery,petrochemical plant, or the like, which collectively may be referred toas a hydrocarbon processing facility.

Crude oil and natural gas deposits typically contain sulfur compoundssuch as H₂S and mercaptans at undesirable levels. For crude oils, sulfurcompound levels must be lowered during the refining process to meetcustomer and regulatory requirements for end-use fuels and lubricants.For natural gas, sulfur levels often must be reduced prior to storage ortransport because sulfur compounds will promote corrosion of componentsof pipelines, storage tank, and processing equipment. Sulfur-based airpollution from the combustion of natural gas may also be of concern andrequire reductions in sulfur levels in natural gas feed stocks prior tocombustion.

In some embodiments, source 650 may include a power plant burninghydrocarbon fuel (e.g., natural gas, oil, and coal) which containssulfur. The power plant outputs combustion exhaust streams includingsulfur-based air pollutants such as H₂S found in or derived from thehydrocarbon fuel. Source 650 may similarly be a combustion engine or aboiler found in a vehicle burning hydrocarbon fuels (e.g., gasoline,kerosene, diesel fuel) including sulfur compounds, and thus consequentlyoutputs combustion exhaust streams including sulfur-based airpollutants. In such instances, filter 600 may be referred to as anexhaust gas filter and such a system may be used to reduce sulfur-basedair pollutants from in the combustion exhaust gas.

Source 650 may also be a fuel storage tank of a vehicle (e.g.,automobile, boat, ship, diesel locomotive, motorcycle, airplane,helicopter, etc.) having a combustion engine or a boiler burning fuelsincluding sulfur compounds. In such instances, filtration system 120 maybe referred to as a fuel filter and may serve to reduce air pollution orengine/boiler corrosion by reducing sulfur compound levels in fuelsprior to combustion. Similarly, source 100 may be an oil reservoir of avehicle having an internal combustion engine. In such instances, thefilter 600 may be referred to as an oil filter.

Source 650 may also be the open atmosphere. Sulfur-based air pollutionon occasion may be at levels which are too high for prolonged exposureby humans, animals, or corrosion sensitive materials such as electronicequipment. In these instances, air handling equipment may incorporatefilter 600 to provide clean air to environment 660.

Environment 660 may, in general, be anything receiving the filteredfluid from filter 600. Environment 660 may be the open atmosphere, when,for example, source 650 is a combustion engine or a power plant. Whensource 650 is the open atmosphere, environment 660 may be a pollutionsensitive environment such as a semiconductor device fabricationfacility, a microelectronic device manufacturing facility, a datastorage center, a server room, a server farm, a electronic componentwarehouse, a hospital ward, archival storage facility, or portionsthereof. When source 650 is a crude oil reservoir or natural gas basin,environment 660 may be, for example, a crude oil storage tank, arefinery, a natural gas storage basin, a LNG processing plant, apipeline, a petrochemical plant, or portions thereof.

FIG. 7 depicts a method 700 for removing sulfur compounds from a fluid.In element 710 of the method, a surface-modified particle is added to afluid. The surface-modified particle may correspond to a particle 100incorporating an HT moiety which reacts with sulfur compounds, asdescribed above.

In element 720 of method 700, the particle may be mixed with the fluid.Element 720 may including stirring the fluid, placing baffles in thefluid flow stream, passing the fluid and particle through in-linemixers, shaking, or otherwise agitating the fluid. Element 720 may beoptional in some embodiments and an active mixing/agitation step may beunnecessary.

In element 730, the particle is separated from the fluid. The separationprocess may involve size-exclusion filters, or the like. Depending onthe size of the particle(s) and viscosity of the filtered fluid, it maybe possible to use a settling of sedimentation process to the separatethe particle(s) from the fluid. Centrifuge systems may also be used, butwould be relatively costly for most applications. Additionally, theseparation process may be a series of different processes such assize-exclusion filtration after a settling process. Also, evaporativemethods and solvent partitioning methods may be incorporated in theseparation process. In some embodiments, the separation process may beunnecessary because it may be sufficient to simply bind the sulfurcompounds to the surface-modified particle to achieve a beneficialresult. For example, when the fluid is a crude oil being prepared forshipment in a pipeline or by a tanker, it may be sufficient for purposesof corrosion prevention to bind the sulfur compounds to thesurface-modified particle to reduce the availability of the sulfurcontaminants in corrosive reactions.

In an example embodiment, the fluid to be filtered may be contained in astorage tank or reaction vessel and a surface-modified particle couldsimply be dumped into the tank or vessel. Depending on size and fluiddensity it may be advantageous to physically mix or stir the fluid. Oncethe particle as been placed in contact with the fluid, sulfursequestering reactions will occur as described previously and sulfurwill be bound to particulate filtration media.

In element 740 of the method, the surface-modified particle may berecovered and reconditioned if desired. After separation of the particlefrom the process fluid, the particle may be recovered, that is, forexample, separated from size-exclusion filter by back-flushing thefilter. The reconditioning process of the particle involves reformationof the HT surface functionalization by removal of the previouslyincorporated sulfur atoms under acidic conditions and then reaction withan HT precursor.

FIG. 8 depicts a method 800 for removing sulfur compounds from a fluid.In an embodiment of method 800, a filter including a surface-modifiedparticle is installed (element 810). In an example embodiment of method800, the filter may correspond to filter 600.

In element 820 of the method 800, the fluid is passed through thefilter. The fluid including a sulfur compound contacts the at least onesurface-modified particle including a HT moiety (e.g., surface-modifiedparticle 100) within the filter. The particle reacts with the sulfurcompound and the sulfur compound is thereby bound to the particle andremoved from the fluid. Element 820 may require pumps, gas compressors,or similar equipment to provide a necessary pressure differentialbetween the intake point and the output point of the installed filter toinduce fluid flow through the filter. The heating or cooling of thefluid may also be necessary, depending on the source of the fluid. Forexample, combustion exhaust gas from a power plant may initially be at avery high temperature and it may be preferable to reduce the temperaturebefore passing the fluid through the filter.

In element 830 of the method 800, the surface-modified particle may bereconditioned. The reconditioning process of the particle involvesreformation of the HT surface functionalization by removal of thepreviously incorporated sulfur atoms and reaction with an HT precursor,for example, exposing the particle to acidic conditions.

It should be noted that a particle may be incorporated into or be aportion of a coating of a substrate. That is, specifically, asurface-modified particle of various embodiments of the presentdisclosure may be incorporated into or be a portion of a coating of asubstrate. A plurality of surface-modified particles according tovarious embodiments may form a coating on a substrate. A substrate inthis context may be, for example, an interior surface of a pipe, anexterior surface of a pipe, a countertop, a surface of a storage tank, amicroelectronic component, a silicon wafer, a printed circuit board, orportions of the foregoing.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiments, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

While the foregoing is directed to embodiments of the present invention,other and further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

What is claimed is:
 1. A surface-attached molecule, comprising:

wherein: LG is a linking group covalently bonded to a nitrogen atom of ahexahydrotriazine moiety and a surface, and AR is an electron-donatinggroup.
 2. The surface-attached molecule of claim 1, wherein theelectron-donating group includes an aromatic moiety.
 3. Thesurface-attached molecule of claim 1, wherein the electron-donatinggroup is a N,N-dimethylamino-p-phenyl group.
 4. The surface-attachedmolecule of claim 1, wherein the electron-donating group is a phenylgroup.
 5. The surface-attached molecule of claim 1, wherein theelectron-donating group is one of a methyl ether, a pyrene, a hydroxylgroup, a sulfhydryl group, or an alkylthio group.
 6. Thesurface-attached molecule of claim 1, wherein the linking group is astraight-chain alkyl group including at least three carbon atoms.
 7. Thesurface-attached molecule of claim 1, wherein the linking group is analkyl silyl group.
 8. The surface-attached molecule of claim 7, whereinthe alkyl silyl group is a propyltriethoxysilyl group.
 9. Thesurface-attached molecule of claim 1, wherein AR is at least one of thefollowing:


10. The surface-attached molecule of claim 1, wherein the surface is anouter surface of a silica particle.
 11. A surface-attached molecule,comprising:

wherein: LG is a linking group covalently bonded to a nitrogen atom of ahexahydrotriazine moiety and a surface, and AR is an electron-donatinggroup, the electron donating group comprising an aromatic moiety. 12.The surface-attached molecule of claim 11, wherein the electron-donatinggroup is a N,N-dimethylamino-p-phenyl group.
 13. The surface-attachedmolecule of claim 11, wherein the electron-donating group is a phenylgroup.
 14. The surface-attached molecule of claim 11, wherein thelinking group comprises a straight-chain alkyl group including at leastthree carbon atoms.
 15. The surface-attached molecule of claim 11,wherein the linking group comprises an alkyl silyl group.
 16. Thesurface-attached molecule of claim 15, wherein the alkyl silyl group isa propyltriethoxysilyl group.
 17. The surface-attached molecule of claim11, wherein AR is at least one of the following:


18. The surface-attached molecule of claim 11, wherein the surface is anouter surface of a silica particle.
 19. A surface-attached molecule,comprising:

wherein: LG is a linking group covalently bonded to a nitrogen atom of ahexahydrotriazine moiety and a surface, wherein the linking groupcomprises a straight-chain alkyl group having at least three carbonatoms, and AR is an electron-donating group, the electron donating groupcomprising an aromatic moiety.
 20. The surface-attached molecule ofclaim 19, wherein the surface is an outer surface of a silica particle.